Joints between components are of great importance in structural design in such industries as aerospace, transportation, and medicine. Mechanically fastened joints leave material discontinuities between components and produce localized, highly stressed areas. Adhesive joints may effectively replace mechanically fastened joints in certain situations. Adhesive joints may form a continuous bond between components, minimizing material discontinuities, and may distribute stress across the bonded joint, minimizing stress concentration. Further, adhesive joints may be tailored to the material properties of the bonded components, e.g., the properties of fiber-reinforced plastics (sometimes referred to as fiber-reinforced polymers or fiber-reinforced composites).
However, adhesion and adhesive joints are less well understood than mechanical fastening mechanisms. Adhesive bond quality is dependent on many factors including chemical bonding, mechanical factors (e.g., interlocking parts), material compatibility, surface preparation, and surface chemistry. Moreover, ensuring and verifying a quality adhesive bond are difficult tasks. Microscopic differences in composition and chemical state may be the difference between a strong bond and a weak bond. Non-destructive testing (e.g., x-ray inspection, ultrasonic inspection) generally indicates only gross material discontinuities but typically fails to indicate adhesion parameters such as chemical state and contamination. Hence, careful characterization of adhesive bonding schemes is important to preparing a quality bond.
Bond quality may be tested by applying forces to a bonded joint until the joint fails. Such destructive testing is impractical for products in service but is suitable for test samples and test coupons embodying a sample adhesive bonding scheme. Adhesion testing protocols designed primarily for metallic components exist (e.g., ASTM D1781 and ASTM D3165 published by ASTM International), but they require precise set-up, calibration, and measurement, and, in some cases, simply are not suitable for adhesion between non-metallic components. Further, adhesion testing protocols typically quantitate the strain energy release rate of a bond as it fails, requiring careful execution of the protocol and measurement of the results. Hence, there is a need for rapid, simplified adhesion testing protocols suitable for non-metallic components, which include simplified determination of results.